For this Edutopia article, Stephen Merrill checked with a number of highly proficient teachers and collected seven comments they use to empower students and create a supportive classroom environment:

• We really missed you yesterday. A student hearing this upon returning from an absence understands that they are a valued contributor to the classroom community. 
• I’m listening. An open-ended invitation to say more is effective – if the teacher doesn’t jump in to fill the silence and if their body language signals that the student has their full attention.
• Oops, I made a mistake. Teachers modeling the comfortable acknowledgement of errors “is essential to academic resilience in students,” says Merrill. Adding humor makes it that much better: That’s a real whopper! or I can’t believe I did that again! Teachers should also praise the thinking behind a student’s creative error.
• I’m sorry. A judicious use of apologies “instantly humanizes the relationship between teachers and students,” says Merrill. It “instills trust, signals respect for the receiver, and makes you more accessible.” 
• We’ll figure it out together. This positions the teacher and student as co-learners, flipping the usual top-down script and giving the student encouragement and agency. 
• You’ve really improved on… “Feedback that is specific, measured, and focused on a student’s process or effort is motivating and actionable,” says Merrill. “Steer clear of feedback that engages in hyperbole, lacks specificity, or praises ostensibly inherent qualities like intelligence.” 
• I believe in you. “Teachers are required to correct papers, hand out grades, and at times chastise poor behavior,” says Merrill. “That power dynamic can subtly undermine students’ self-confidence.” Periodically expressing belief in students’ individuality and high expectations for their success can get things back on an even keel.
“7 Things Teachers Say to Create a Supportive Classroom” by Stephen Merrill in Edutopia, August 26, 2021